LibGfx: Add TGA Loader :^)

This patch adds a basic TGA Loader. Currently it can only handle
uncompressed files with a bit depth of 24 or 32 bits per pixel.

Userland/Libraries/LibGfx/CMakeLists.txt

@@ -50,6 +50,7 @@ set(SOURCES
     SystemTheme.cpp
     TextDirection.cpp
     TextLayout.cpp
+    TGALoader.cpp
     Triangle.cpp
     WindowTheme.cpp
 )